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Re: [PATCH] rvalue reference implementation for C++0x

On 3/10/07, Russell Yanofsky <> wrote:
> I'd rather not expose the concept of an rvalue reference to the back
> end, its semantics should be encapsulated by the front end.  I think the
> right answer is to have a wrapper for build_reference_type_* in the
> front end to handle the extra semantics.
> I'm not sure what the best coding strategy is for this.  One option
> would be to establish a convention of putting the rvalue ref after the
> non-rvalue ref in the TYPE_NEXT_REF_TO chain, or in some other field if
> there are others free, so that the C++ front end function can call the
> back end function and then use the result to look up the rvalue version.

It seems to me like everything you said is already implemented. Rvalue
reference types become part of the TYPE_NEXT_REF_TO chain just like
other variants of reference types. And build_reference_type() is the
front-end wrapper for the build_reference_type_for_mode() function.

I think Jason is saying something different. TYPE_REF_IS_RVALUE is a flag defined in tree.h, which is used by several front-ends and the middle-end, although the rvalue references features itself is a C++0x-only notion. Jason is saying that it would be better if we could keep *all* of the changes in the C++ front end, and not touch any of the common bits (tree.c, tree.h). He's suggesting a way that one could implement a new wrapper around build_reference_type, say, cp_build_reference_type (tree type, bool rval) just in the C++ front end. cp_build_reference_type could use the convention he mentions based on TYPE_NEXT_REF_TO to make the rvalue reference of a type easily found by this function in the C++ front end while not disturbing the other front ends or the middle end.


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